Just one of my many fun throwaway projects :P It used to be up at skrch.com, but went down a while ago. Couldn't figure out how to monetize/sell it so I moved on -- I'm still not sure what sector could use something like it. The original idea actually came about in a dream (true story!) and I wondered if I could actually implement it. Took me about a month or two as I had never used OpenCV before.
The search was done with a very simple histogram analysis algorithm and the image database had about 10,000 pictures from Flickr. Results were pretty decent, but sometimes hit and miss[1]. Database costs were pretty high as I don't think there's any database out there that has any way to efficiently hash 2d histograms (so everything was stored in memory). That could be a fun challenge.